Conditional Tags and Parent/Child pages

Is it possible to use conditional tags to cover all the pages that have a particular parent? For example, if I have a parent page with the slug “about” and I create three child pages of “about” named “vita” “contact” and “portfolio”, how would I use conditional tags to cover all of these pages. Using if is_page(‘about’) doesn’t do the trick.

Basically, I want to change the content of my sidebar based on what parent the child page is under. Here’s my script for the sidebar:

<div id=”sidebar”>

<!– PHP includes for the sidebar…uses different include files depending on what part of the site is being viewed. –>

I did a search, and all I could find relevant is here. I’m familiar with using conditional tags. I know I could just write an if is_page() for every page I make, but I’d rather cover it by just specifying the parent page.